1. Field of the Invention
The present invention relates to a webbing retractor which structures a seat belt device for restraining, by an elongated, strip-shaped webbing belt, the body of a vehicle occupant who is seated in a seat of a vehicle or the like.
2. Description of the Related Art
A seat belt device which restrains, by an elongated, strip-shaped webbing belt, the body of a vehicle occupant who is seated in a seat of a vehicle, is equipped with a webbing retractor which is fixed to the vehicle body at the side of the seat. The webbing retractor has a spool whose axial direction runs, for example, substantially along the longitudinal direction of the vehicle. The proximal end side, in the longitudinal direction, of the webbing belt is anchored at the spool. The spool can take up the webbing belt in the form of a roll around the outer peripheral portion of the spool. When the seat belt device is not being used, the webbing belt can be taken-up and accommodated on the outer peripheral portion of the spool.
An urging member, such as a spiral spring or the like which urges the spool in a take-up direction in which the spool takes up the webbing belt, is provided at the webbing retractor. Due to the urging force of this urging member, the webbing belt is taken up and accommodated. In the state in which the webbing belt is applied to the body of a vehicle occupant, slack or the like of the webbing belt is eliminated by the urging force of the urging member.
On the other hand, a mechanism has been conceived of which, when the vehicle rapidly decelerates or the like, takes-up a given amount of the webbing belt onto the spool, so as to eliminate the slight looseness called “slack”, and increase the force by which the webbing belt restrains the body of the vehicle occupant, and even more reliably hold the body of the vehicle occupant. In this type of mechanism, generally, the state of rapid deceleration of the vehicle is detected by an acceleration sensor, and the driving force of a driving mechanism, such as a motor or the like, forcibly rotates the spool in the take-up direction on the basis of an electric signal from the acceleration sensor (refer to the Japanese Patent Application Laid-Open No. 2001-347923 as an example of a so-called “motor retractor”).
In contrast, a structure has been thought of in which the distance to another vehicle or an obstacle ahead is detected by a distance sensor or the like. When the distance to the vehicle or the obstacle ahead is less than a given value, a motor is operated, and the spool is rotated in the take-up direction by the torque of the motor.
Incidentally, in the case of the above-described motor retractor, a structure, in which a clutch is interposed between the output shaft of a motor and a spool and only the rotation from the output shaft side is transmitted to the spool by this clutch, is adopted in order to prevent the transmission of the rotation from the spool side to the motor.
However, in motor retractors which have been used until now, the clutch is disposed at the outer side of the frame and at the side of one leg plate of the pair of leg plates which structure the frame. Therefore, in a case in which the output shaft of the motor is connected to the clutch, the motor must be disposed at the side of the leg plate at which the clutch is provided, which side is opposite the side at which the other leg plate is disposed, i.e., the motor must be disposed at the side of the leg plate and at the outer side of the frame, or must be disposed further toward the top of the frame or the bottom of the frame than the pair of leg plates. In the case of such a structure, the motor retractor itself becomes large due to the parts which are relatively heavy, such as the motor, being positioned at the outer side of the frame, or above or below the frame. There is therefore the disadvantage that the overall balance of weight of the motor retractor is poor.